I think it's a very fair question.
Here's my honest answer:
If you're mostly into digital media, at the iLife level, the truth is that the same thing won't be that bad on top of Windows. You can keep using iTunes, and Picasa is a very competent and free alternative to iPhoto. If you use Adobe, well, then, it'll pretty much be the same regardless of which OS you use it on top of.
So the pros and cons come pretty much down to how much you can like the way the OS does things.
If you use Windows -> lower hardware cost in some circumstances, the OS is what it is (both of us have plenty of experience with it), you'll have more hardware compatibility, but you'll have to deal with viruses and spyware and so on. If you turn on the firewall, use Firefox instead of IE whenever humanly possible, and get AV software, this isn't so bad.
If you use OS X -> sometimes higher hardware cost, but with more "stuff" bundled in. Fewer compatible pieces of hardware, but almost all of them work in true "plug n' play" fashion, which is a beautiful thing. Lots of little things that are important to artists -- like color calibration -- are built into OS X in a much more accessible way than in Windows XP. Essentially no viruses or malware. But you'll have to deal with Apple paternalism.
In terms of the paternalism -- all this "do it the Apple way, because they're designers" stuff... I think the best thing to tell yourself is to swallow your pride, and invest a month or two really trying to just go with Apple's flow. If you keep kicking back, you'll probably be happier with Windows. Or you might find that you like it. The big question is whether it gets in the way of true creativity -- if you are enjoying your photography and your music less because of the way the OS works, then run away, whatever the OS is.
But then again, if you use iTunes and Picasa, then they are going to do almost the same thing to you on Windows that iTunes and iPhoto do to you on OS X, in terms of telling you how to store files and so on. And considering that they own most of your files.... Well.....
So I dunno. In a year or so, Vista will wrinkle the picture further. In the long run I think it will be a big boost for Windows.
For me personally, when I took that dive, and tried things Apple's way, I found that I liked the trade. Plus I was always drawn by the industrial hardware design aesthetic, and for the most part, I can buy off on the price premium for it.
So that's my rambling insight. Good luck!
